Many different types of data storage and handling systems exist and are being used to store data cartridges at known locations and to retrieve a desired cartridge so that data may be written to or read from the data cartridge. Such data storage and handling systems are often referred to as "juke box" data storage systems, particulary if they can accommodate a large number of individual data cartridges.
While the data cartridges may be arranged within the data storage system in any of a wide variety of configurations, many juke box data storage systems are designed so that the data cartridges are stored in one or more vertical stacks or arrays. If so, the data storage system is usually provided with positioning apparatus for moving a cartridge access device up and down the array of cartridges so that the cartridge access device can access selected data cartridges stored in the array. Depending on the particular system, the cartridge access device may comprise a cartridge engaging assembly or "picker" which may be adapted to engage the selected data cartridge, withdraw it from the array, and carry it to a cartridge read/write device located elsewhere within the system. The read/write device may then be used to read data from or write data to the cartridge. Once the read/write operation is complete, the cartridge engaging assembly or picker may withdraw the data cartridge from the read/write device and return it to the appropriate storage location. In another type of system, the cartridge access device may comprise the read/write device itself, in which case data cartridge may be read from or written to without the need to carry the data cartridge to a separate read/write device.
Regardless of the particular type of cartridge access device that is utilized by the data storage system, the positioning system must be capable of moving the cartridge access device along the cartridges stored in the array so that the desired cartridge may be accessed. One type of positioning system, often referred to as a "lead-screw" system, mounts the cartridge access device on a lead-screw, which when turned, moves the cartridge access device up and down along the array of cartridges. While such lead-screw positioning systems are being used, they are not without their problems. For example, in such a system the cartridge access device is often cantilevered on the lead-screw. Such a cantilevered mounting arrangement tends to allow excessive transverse or rotational movement of the cartridge access device which reduces positional accuracy and may make it difficult for the cartridge access device to engage the desired data cartridge.
Partly in an effort to solve the foregoing problems, positioning systems have been developed which utilize separate guide rails or tracks to guide the cartridge access device across the array of cartridges. The cartridge access device is mounted to the separate guide rails or tracks and the lead-screw is then used only to move the cartridge access device to the desired location. While such systems generally provide for increased positional accuracy over the cantilevered type of lead-screw positioning systems, they are still not without their disadvantages. For example, the guide rail or track assemblies are usually precision machined components, which adds to the overall cost of the data storage system. Moreover, the guide rail or track assemblies are often difficult to align and may become mis-aligned during subsequent shipping or movement of the cartridge handling device. If the mis-alignment is substantial, it may be necessary to re-align and re-calibrate the positioning system before the data storage system can be placed in operation.
Consequently, a need remains for a positioning system for moving a cartridge access device across an array of cartridges that provides increased positional accuracy to reduce errors due to misalignment of the cartridge access device. Such increased positional accuracy should be achieved with a minimum number of components to maximize reliability, yet not require the use of expensive, precision machined components and guide rails. Additional advantages could be realized by reducing the amount of time required to align and calibrate the assembly during production and by reducing the likelihood of subsequent mis-alignment, such as may occur during shipping or from rough handling. Ideally, the positioning system should be made as small as possible so that it may be mounted in a relatively small space within the data storage system.